1. Field of the Invention
This invention is generally directed to a device for the generation of auxiliary pressure, particularly for automotive vehicles.
2. Description of the Related Art
Such a device is generally known from German Published Patent Application (DE-OS) No. 32 34 182. The known device provides reciprocating movement of a hydraulically actuated differential piston for driving a pump piston which delivers a pressure medium from a tank to a consumer. To this end, a reversing valve required for cyclic reversal is hydraulically or pneumatically actuated via the differential piston so that the atmospheric pressure, or the vacuum of a vacuum source, is active at the differential piston to stimulate the oscillating pumping movement of the differential piston.
The described design of the differential piston in the known device as a control unit for the hydraulic or pneumatic actuation of the reversing valve, has the disadvantage of a decidedly expensive and intricate construction because of the requirement of a reversing valve arranged indirectly (or possibly even separately) with respect to a sleeve-shaped differential piston provided with recesses. Also, the referenced control unit is disadvantageous because of the requirement of a line system for automatically activating the reversing valve. Further, there is the danger of malfunctions such as even small leakages resulting from known problems of manufacture and of sealing, if, during operation of the device, the differential piston, or rather the actuating piston, is of the control slide type.
The cost factor, in particular, implies considerable disadvantages in the known system. Further yet, there exists the danger that the differential piston will remain stationary in a position between the two dead center positions in the event that control currents are unsteady, thereby preventing any switching of the control valve.
Accordingly, it is an object of this invention to provide an improved device for driving an auxiliary pressure generator of the generally known type described above, in which the most simple constructional means are employed for increasing reliability independently of disadvantageous material and constructional phenomena resultant from manufacture and use.
It is a further object of the invention to simultaneously minimize the cost of manufacturing of the device.